Stubborn Problem.

[ChrisMills]

Hi Guys,

 

 I'm brand new to the forum. 1st. post. I've run into a problem that's got me stumped for the moment.

 

 Vehicle info: 2004 GMC Sierra 2500 HD, 6.0l. auto trans,4WD, 44,000 miles

 

 Background: It was a company truck used for mostly plowing a paved parking lot & hauling the trash trailer to the dump. I picked it up as a project truck about six months ago. It's in reasonably good shape for it's age but needs a number of small fixes to pass state inspection. The heft of the wear & tear seems to be around the steering column. The key cylinder isn't quite right and the spring on the transmission shift lever broke. It would occasionally throw a passlock and there might have been a parasitic battery drain. It became SOP to disconnect the negative battery terminal when the truck wasn't in use. I rebuilt the instrument cluster and that apparently cleared up the battery drain issue.

 

 The problem at hand: I went out to start the truck a few months ago and it went into reduced engine power mode. I turned the key to the off position, removed the key, and the truck kept running with the cluster lights flashing. I can't seem to get past this problem.

 

 Remedial measures taken to date:

 

1: Checked all fuses for continuity.

2: Cleaned up every ground that i can find.

3: Replaced the ignition switch.

4: Replaced the headlight switch.

5: Replaced the TPS and it's electrical connector.

6: Downloaded the trouble codes. They relate to the throttle body TPS & transmission solenoid

7: Replaced the PCM ( The trouble codes soon returned after the passlock re-learn procedure performed.)

 

Summary:

 It seems to be a power issue of some kind at this point. Maybe something is backfeeding ? Maybe something that controls the power is sending it in the wrong direction at the wrong time ? Could it possibly be the BCM ?

 

 At this point i'm leaning toward wear & tear in the ignition lock cylinder & ignition lock cylinder housing as being the culprit. Maybe the gearing in there is worn and not engaging the ignition switch correctly ?

 

 I wish i knew more about how it all works. Could really use the advise of someone that works in the trade every day and has seen this problem in the 2004 model range trucks before. Maybe there were some TSB's released on the issue ?

 

 Any help would be sincerely appreciated.

[Jglew82]

First of all, can you provide the trouble codes your pulled from the vehicle?   

[riverbanks]

One on here a while back had critters chewing wires under relay center under the hood,so insulation was compromised on wires and touching each other,give that a look

[ChrisMills]

 Okay, i just performed a fresh diagnostic so that all of the trouble codes would be current.

 

 I used BlueDriver all systems check with engine on and transmission in park.

 

                              1 Confirmed Trouble Code

 

U0107 Lost communication with Throttle actuator "A" control module.

 

                            2 Pending trouble codes

 

P0141 O2 sensor heater circuit bank 1 sensor 2

U0107 Lost communication with throttle actuator "A" control module

 

                             2 Powertrain codes

P0141

U0107

 

                              1 Shared Address Module Code

 

B1440 Status: History, Power mode master input circuits mismatch

 

                              1 airbag code

U1000 Status: History, Class 2 data link malfunction

 

                             2 Radio codes

U1000

 

B1035

 

 That's about everything that i have for now in the way of trouble codes.

 

 I've got some time today so i will go pull the underhood relay center and check for any problems there. There was evidence that something small and furry pulled out some of the fiberglass on the engine side of the firewall when it was a company truck. I think they caught that one early. Found a small nest of made of insulation under the plastic cowl that sits on top of the engine. (It might have resettled under the relay center.)

 

 

 

[Jglew82]

Oooh yeah, check for munched up wires! 

[ChrisMills]

 Allright ... so i pulled the under hood fuse / relay box. There's no sign of any damage to the wiring. No corrosion on any of the contacts. No sign that a critter was living in there. I pulled all of the relays and tested them just because i was there anyway.

 

 The only thing i did find was that pin 30, where the ignition relay plugs in, showed about 12.5 volts.

 

 Is that supposed to be de-energized with the ignition off and the key removed ?

[Hazcat]

U0107 Lost communication with throttle actuator "A" control module.

 

"There's your problem lady!"

 

 

Where do you live? Did you get this fixed yet?